matplotlib-users

[Matplotlib-users] custom markers from images?

[C M <cmp...@gm...>]

I'd like to use, in one case, small loaded images (pngs) as markers on an
interactive matplotlib plot (using the OO approach).  I'd potentially like
to be able to point-pick these markers, too, as well as have them update
appropriately if the plot is resized.

The only example I've been to find of this is here:
http://stackoverflow.com/questions/2318288/how-to-use-custom-marker-with-plot

But that is from 2 years ago.  Is this way of doing it--which the author
describes as a "kludge"--still the state of things, or is there a better
approach now?  (And right now this way isn't working for me...the images
are down the bottom of the figure).

Thank you,
Che

Re: [Matplotlib-users] custom markers from images?

[Benjamin R. <ben...@ou...>]

On Wed, Feb 29, 2012 at 5:47 PM, C M <cmp...@gm...> wrote:

> I'd like to use, in one case, small loaded images (pngs) as markers on an
> interactive matplotlib plot (using the OO approach).  I'd potentially like
> to be able to point-pick these markers, too, as well as have them update
> appropriately if the plot is resized.
>
> The only example I've been to find of this is here:
>
> http://stackoverflow.com/questions/2318288/how-to-use-custom-marker-with-plot
>
> But that is from 2 years ago.  Is this way of doing it--which the author
> describes as a "kludge"--still the state of things, or is there a better
> approach now?  (And right now this way isn't working for me...the images
> are down the bottom of the figure).
>
> Thank you,
> Che
>
>
Yeah, there are better ways to do that, somewhat.  The problem with the
proposed solution is that it relies on non-public APIs, which are can be
subject to change without deprecation.  Instead, I would have created the
figimage object with a particular transform object that would have placed
it at the appropriate data points.  Perhaps someone else on this list knows
of the correct way to do that?

Ben Root

Re: [Matplotlib-users] custom markers from images?

[C M <cmp...@gm...>]

> Yeah, there are better ways to do that, somewhat.  The problem with the
> proposed solution is that it relies on non-public APIs, which are can be
> subject to change without deprecation.  Instead, I would have created the
> figimage object with a particular transform object that would have placed
> it at the appropriate data points.


Maybe your or someone from this list can help me understand more about
this.  So, if I take the code that I have adapted to my purposes, there are
questions I have about it:

        # constants
        dpi = 72; imageSize = (32,32)
        # read in our png file
        im = image.imread('redX_10.png')

So far, so good--just setting the dpi and getting the image.

        fig = self.figure
        ax = self.subplot
        ax.get_frame().set_alpha(0)

Does the current version of Matplotlib require the frame be set to fully
transparent?  I need a white canvas, so I think I'd rather not do that.

        # translate point positions to pixel positions
        # figimage needs pixels not points
        line = self.line_collections_list[0][0]

"line" here is my line of datapoints from elsewhere in my app.

        line._transform_path()
        path, affine =
line._transformed_path.get_transformed_points_and_affine()
        path = affine.transform_path(path)

I have no understanding of the purpose of the previous three lines.  Can
someone give me a quick explanation?

        for pixelPoint in path.vertices:
            # place image at point, centering it

fig.figimage(im,pixelPoint[0]+80,pixelPoint[1]+180,origin="upper")

This is just a way to put the image somewhere on my canvas to see it, so
these offsets are just for this exercise.

I should state that if I do it this way, the images appear on the canvas
but are NOT repositioned in data coordinates (and they should be)--which is
probably just Ben's point, right?

Thanks,
Che

Re: [Matplotlib-users] custom markers from images?

[Benjamin R. <ben...@ou...>]

On Thu, Mar 1, 2012 at 1:11 PM, C M <cmp...@gm...> wrote:

>
> Yeah, there are better ways to do that, somewhat.  The problem with the
>> proposed solution is that it relies on non-public APIs, which are can be
>> subject to change without deprecation.  Instead, I would have created the
>> figimage object with a particular transform object that would have placed
>> it at the appropriate data points.
>
>
> Maybe your or someone from this list can help me understand more about
> this.  So, if I take the code that I have adapted to my purposes, there are
> questions I have about it:
>
>         # constants
>         dpi = 72; imageSize = (32,32)
>         # read in our png file
>         im = image.imread('redX_10.png')
>
> So far, so good--just setting the dpi and getting the image.
>
>         fig = self.figure
>         ax = self.subplot
>         ax.get_frame().set_alpha(0)
>
>
>
Does the current version of Matplotlib require the frame be set to fully
> transparent?  I need a white canvas, so I think I'd rather not do that.
>
>
I think this is technically because of the use of figimage.  Any axes that
are created would get plotted above the figimage.  I suppose one could
manually set the zorder to a high enough number to make sure it stays on
top.


>         # translate point positions to pixel positions
>         # figimage needs pixels not points
>         line = self.line_collections_list[0][0]
>
> "line" here is my line of datapoints from elsewhere in my app.
>
>         line._transform_path()
>         path, affine =
> line._transformed_path.get_transformed_points_and_affine()
>         path = affine.transform_path(path)
>
> I have no understanding of the purpose of the previous three lines.  Can
> someone give me a quick explanation?
>
>
The transforms framework translates coordinates from one system to
another.  There are multiple coordinate systems within a mpl figure.  data,
axes and figure are the three main "reference frames".  I think the first
line is effectively useless (but due to caching has no impact on
performance).  The second line would translate the coordinates stored in
"line" into figure-relative coordinates, and also provide a special object
for doing affine transformations.  The point of that step, IIUC, is to do a
special handling of curves (either the line data itself has curves, or the
coordinate tranformation has curves).  Consider the case of drawing a
straight line from a Lat/Lon coordinate on a map to another Lat/Lon
coordinate (so, there are only two points in "line").  Now, that line may
not be straight depending upon the map projection used, so the final line
may need many more points to represent it correctly in a transformed
projection.  Again, I am not an expert here, so it is quite likely that I
mixed something up.



>         for pixelPoint in path.vertices:
>             # place image at point, centering it
>
> fig.figimage(im,pixelPoint[0]+80,pixelPoint[1]+180,origin="upper")
>
> This is just a way to put the image somewhere on my canvas to see it, so
> these offsets are just for this exercise.
>
> I should state that if I do it this way, the images appear on the canvas
> but are NOT repositioned in data coordinates (and they should be)--which is
> probably just Ben's point, right?
>
>
Right.  It should be technically feasible to just simply tell figimage to
use a different transformation object, but this might have implications
elsewhere.  I am very hazy in this part of mpl.

Cheers!
Ben Root

Re: [Matplotlib-users] custom markers from images?

[C M <cmp...@gm...>]

> Right.  It should be technically feasible to just simply tell figimage to
> use a different transformation object, but this might have implications
> elsewhere.  I am very hazy in this part of mpl.
>

Hmm, I've simplified the figimage to just this line:

        fig.figimage(im,100,100,origin="upper", transform=None)

And it puts the image 100 up and 100 px out from the lower right corner.  I
then tried setting the transform from None to all the various possible
transforms listed on this page:

http://matplotlib.sourceforge.net/users/transforms_tutorial.html

as well as their inverted() forms.  None of them allowed the image to be
updated with data coordinates when the plot was resized.

It really seems that figimage is a property of the figure only and not the
canvas, so whatever the axes do is irrelevant to its placement.

But I really don't know for sure.  So far, this isn't going to work this
way.

Thanks,
Che

Re: [Matplotlib-users] custom markers from images?

[C M <cmp...@gm...>]

I've for now taken a different approach that means I won't need custom
markers from images.

But I'm just curious:  is there any wish/plans in Matplotlib to add support
for this?  I think it could do a lot to expand what's possible in terms of
the look and feel of plots (even without things drifing into USA Today
territory!).

Just my $0.02

Che

Re: [Matplotlib-users] custom markers from images?

[Michael D. <md...@st...>]

It would be a nice idea.  I'm not sure it's something that would work 
terribly well in vector backends as the images may not scale well.  I 
should mention that there is already support to use arbitrary Unicode 
characters or math expressions as markers already, which does work well 
in vector backends.

Mike

On 03/07/2012 01:59 PM, C M wrote:
> I've for now taken a different approach that means I won't need custom 
> markers from images.
>
> But I'm just curious:  is there any wish/plans in Matplotlib to add 
> support for this?  I think it could do a lot to expand what's possible 
> in terms of the look and feel of plots (even without things drifing 
> into USA Today territory!).
>
> Just my $0.02
>
> Che
>
>
> ------------------------------------------------------------------------------
> Virtualization&  Cloud Management Using Capacity Planning
> Cloud computing makes use of virtualization - but cloud computing
> also focuses on allowing computing to be delivered as a service.
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>
> _______________________________________________
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Re: [Matplotlib-users] custom markers from images?

[Jae-Joon L. <lee...@gm...>]

One way to use images as a marker would be to use offsetbox module.
Here is an example adopted from

http://matplotlib.sourceforge.net/examples/pylab_examples/demo_annotation_box.html

Regards,

-JJ


import matplotlib.pyplot as plt
from matplotlib.offsetbox import OffsetImage, AnnotationBbox
from matplotlib.cbook import get_sample_data

import numpy as np

if 1:
    fig = plt.gcf()
    fig.clf()
    ax = plt.subplot(111)


    xy = [0.3, 0.55]

    arr = np.arange(100).reshape((10,10))
    im = OffsetImage(arr, zoom=2)

    ab = AnnotationBbox(im, xy,
                        xycoords='data',
                        pad=0.3,
                        )

    ax.add_artist(ab)


    # another image


    from matplotlib._png import read_png
    fn = get_sample_data("lena.png", asfileobj=False)
    arr_lena = read_png(fn)

    imagebox = OffsetImage(arr_lena, zoom=0.1)

    xy = (0.7, 0.4)
    ab = AnnotationBbox(imagebox, xy,
                        xycoords='data',
                        pad=0.5,
                        )


    ax.add_artist(ab)

    ax.set_xlim(0, 1)
    ax.set_ylim(0, 1)


    plt.draw()
    plt.show()




On Thu, Mar 8, 2012 at 4:25 AM, Michael Droettboom <md...@st...> wrote:
> It would be a nice idea.  I'm not sure it's something that would work
> terribly well in vector backends as the images may not scale well.  I should
> mention that there is already support to use arbitrary Unicode characters or
> math expressions as markers already, which does work well in vector
> backends.
>
> Mike
>
>
> On 03/07/2012 01:59 PM, C M wrote:
>
> I've for now taken a different approach that means I won't need custom
> markers from images.
>
> But I'm just curious:  is there any wish/plans in Matplotlib to add support
> for this?  I think it could do a lot to expand what's possible in terms of
> the look and feel of plots (even without things drifing into USA Today
> territory!).
>
> Just my $0.02
>
> Che
>
>
> ------------------------------------------------------------------------------
> Virtualization & Cloud Management Using Capacity Planning
> Cloud computing makes use of virtualization - but cloud computing
> also focuses on allowing computing to be delivered as a service.
> http://www.accelacomm.com/jaw/sfnl/114/51521223/
>
>
>
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>
>
>
> ------------------------------------------------------------------------------
> Virtualization & Cloud Management Using Capacity Planning
> Cloud computing makes use of virtualization - but cloud computing
> also focuses on allowing computing to be delivered as a service.
> http://www.accelacomm.com/jaw/sfnl/114/51521223/
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>